Transcript for 4 People Dead, Including Alleged Gunman, in Fort Hood Shooting

cc1 Test message Breaking news tonight, a mas shooting on a army base 16 injured and four dead, including the gunman. The shooter, a U.S. Soldier, a combat veteran and a married father. Seep yor justice correspondent Pierre Thomas joins us now. Good evening, Pierre. Tonight, our source tonight are identifying the suspect as Ivan Po less, 34 years old. He's an Iraq war veteran apparently suffering from mental health issues. And sources believe that played a critical role in the bloody rampage that happened today. Seek shelter immediately. Reporter: That was the word that first went out late this afternoon at ft. Hood. Gripped by chaos and fear for hours after a lone gunman open fired on the army base outside of Killeen, Texas. It's scary. Reporter: He was described as a truck driver struggling with mental health issues. It's believed he walked into one of the unit buildings, open fired, got into a vehicle, fired from the vehicle, got out of the vehicle, walked into another building and open fired again, and was engaged by local law enforcement here at ft. Hood. He died at the scene after a confrontation with police. He was approaching her at about 20 feet. He put his hands up then reached under his jacket, pulled out the .9 mill, and she pulled out her weapon and then she engaged and then he put the weapon to his head and he died of a self-inflicted gunshot wound. It was clearly heroic what she did. At that moment in time, and she did her job and did exactly what we would expect from a united States army military police. He had served in Iraq for four months in 2011. The suspected weapon, a .45 caliber smith and Wesson recently purchased in the area, not registered at the base. The soldier is married, does have family, and we're in the process of notificatinotification. Many of those were rushed to the hospital in temple. They have a variety of injuries we've been treating, ranging from gunshot wounds that involved extremity, abdomen, chest and neck. Law enforcement including the FBI cleared the base tonight of any other possible threats. While the investigation is still ongoing, there are no indications this was an act of terrorism. The suspect had been in treatment. He self-reported a draw mattic brain injury. He was not diagnosed today with PTSD. He was undergoing a diagnosis process to determine if if he had PTSD. He was undergoing behavioral health for depression and anxiety and a variety of other psychological and psychiatric issues. We're heart broken that something like this might have happened again. President Obama pointed out many of the servicemen and women at ft. Hood recently returned from serving overseas. The folks there sacrificed so much on behalf of our freedom. Many of the people there have been through multiple tours in Iraq and Afghanistan. When they're at their own base, they should feel safe. An ear rery meeerie reminder of what happened in 2009 in ft. Hood when hassan went on a rampage. It was the worst shooting ever on a military base. Most of the soldiers preparing to head to war when hassa in T walked in and open fired. The victims were unarmed and unable to defend themselves. Stun missing. As I've gone to the hospital, soldiers and family members and many of the great civilians with are absolutely devastated. A responding police officer final open fired, paralyzing hassan from the waste down. Last year, hassan was found guilty on all 13 counts of premeditated murder and had been on death row at fort Leavenworth since August. Since then, there have been at least nine other shootings at U.S. Military bases. And last year, a former Navy reservist and military subcontractor, Aaron Alexis fatally shot 12 people at the Washington Navy yard. A large portion of the city, only miles away from the white house was on lockdown before lex lexis was shot and killed. A man took a gun from a guard before security personnel shot and killed him. All this raising serious questions about security at U.S. Ma military bases. These are very hard to stop. And Dan, what makes us all the more tragic is what happened in ft. Hood, which is still healing from that unspeakable tragedy of five years ago.

This transcript has been automatically generated and may not be 100% accurate.

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